This present invention relates to a hemming apparatus for closures to be used on vehicles, such as trunks, deck lids, hoods, sliding doors, and other doors.
Typically, a closure, such as a door includes an inner panel and an outer panel. The inner panel of a door is typically a thicker gage than the outer panel. The inner panel provides the structural integrity and support for hinges and the like, while the outer panel generally is considered to be a cosmetic outer skin. Structurally, everything is connected to the inner panel for support. When assembling the outer panel to the inner panel of a door, the two separate panels are positioned with respect to one another in a hemmer apparatus. In the hemmer apparatus, the outer peripheral edge of the outer panel is rolled and bent over the inner panel to connect the two panels to one another.
In the past, it was common to weld the outer panel to the inner panel, however, with thin gauge materials, welding produced visible defects in the outer panel which was unacceptable to automotive manufacturers. As a result, it became common to adhesively secure the inner and outer panels to one another. The adhesive bonding of the two panels has typically been accomplished with either a one part adhesive, or a two part epoxy adhesive. The one part epoxy adhesive is heat curable (requiring heat in excess of 240xc2x0 in order to cure), while the two part epoxy adhesive is time sensitive and takes approximately 35 to 40 minutes to tack and fully cure within a day. Historically the hemmer apparatus brings the two panels together at a xe2x80x9cmarriage stationxe2x80x9d or a xe2x80x9chemmer stationxe2x80x9d and produces a seam all the way around and rounds out the edges so there are no sharp edges on the closure, and establishes the geometry that fits the inner and outer panels with respect to one another. There typically are no welds that take place inside a hemmer apparatus, so the inner and outer panels have a tendency to shift with respect to one another as the closure is processed along the production line. The biggest problem with the one part adhesive is that it doesn""t cure until the body in white is painted, which raises the temperature sufficiently to cure the heat sensitive one part adhesive. Up until that point in time, the geometry of the inner panel with respect to the outer panel can shift and the curing process can set the final geometry of the two panels with respect to one another in an improper shifted relationship. The one part epoxy adhesive is desirable currently, since it costs approximately $5 per gallon.
The two part epoxy adhesive costs approximately $12 per gallon and is more difficult to apply, since two parts of the adhesive must be mixed and applied to one of the opposing surfaces of the closure. Furthermore, the two part epoxy adhesive tack cures in approximately 30 minutes. While this is significantly faster than the one part adhesive, it does not guarantee accurate positioning of the two panels with respect to one another. For example, if an operator takes the assembled inner and outer panels out of the hemmer and places the assembly on a rack, the two panels may shift with respect to one another prior to the two part epoxy adhesive curing completely. Since the one part adhesive is more desirable from a cost perspective, the industry has attempted to quickly heat cure at least portions of the one part adhesive by applying localized heat to limited portions of the panel assembly at a work station immediately after the hemmer apparatus. Heat coils typically were provided at predetermined locations around the periphery of the panel assembly in order to cure localized areas of the one part adhesive prior to further processing of the panel assembly. While this procedure was an improvement, it still did not guarantee accurate and true positioning of the inner panel with respect to the outer panel. The assembled panels were still subject to dislocation with respect to one another while being transferred from the hemmer apparatus to the localized heat application work station.
It is desirable in the present invention to temporarily fix the relative position and geometry of the inner panel and the outer panel while in the geometry fixture of the hemmer apparatus, so that the orientation of the assembled panels with respect to one another is not lost prior to curing of the one part adhesive. The present invention welds the inner panel and the outer panel with respect to one another in a plurality of locations around the peripheral, folded-over, hemmed edge while the panels are held in the proper geometry with respect to one another in the hemmer apparatus. The laser weld according to the present invention can include a fillet weld on the peripheral edge of the return of the hem between the inner panel and the outer panel and/or a spot weld on the return of the hem. In the present invention, this is referred to as a geometry weld. The present invention provides a plurality of geometry welds to freeze the geometry while still using an adhesive, such as the one part adhesive to provide the permanent connection between the panels after curing. The manufacturing tack weld according to the present invention holds the relationship between the inner panel and the outer panel until the adhesive is cured in the paint oven.
Alternatively, according to the present invention the adhesive can be eliminated and the structure of the door can be permanently welded at a station immediately following the hemmer apparatus where the manufacturing tack welds are provided to freeze the geometry. In either case, a plurality of tack welds, such as four, six, eight, or more, depending on the configuration of the two panels, are provided to establish and maintain the geometry between the inner panel and the outer panel during assembly. The plurality of tack welds are provided in the hemmer apparatus where the geometry is established, the hems are rolled over, and optics are provided at various locations to put the weld into the hem of the assembly while still maintained with the proper geometry in the hemmer station. The manufacturing tack geometry welds are provided at spaced locations around the periphery to lock the geometry of the assembly in place.
Other objects, advantages and applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.